A motor-vehicle engine system will typically include an engine-driven coolant pump (known also as a ‘water pump’). The coolant pump circulates liquid coolant through jackets that surround the cylinder head or block of the engine to provide continuous cooling during engine operation. Recent coolant-pump configurations recognize the advantage of allowing the pumping rate—thus, the rate at which heat is carried away by the coolant—to vary with changing engine conditions. Specifically, after the engine has warmed to its normal operating temperature, it is desirable to operate the coolant pump in proportion to engine speed so that overheating is avoided and the normal operating temperature is maintained. When the engine is quite cool, however—e.g., following a cold start—cooling in proportion to engine speed may not be desirable. Instead, it may be desirable to allow the engine to warm to its normal operating temperature as quickly as possible. This strategy provides fuel-economy benefits deriving from faster viscosity reduction of the engine lubricant, which lowers friction, and faster warming of the intake air charge, which reduces pumping losses and increases EGR tolerance. Prompt engine warm-up also promotes faster catalyst light-off in the exhaust system, for improved emissions-control performance.
Accordingly, German patent application DE 10 2010 043 264 A1 describes an engine-driven coolant pump in which rotational motion from the crankshaft of the engine is transmitted through a fluid coupling to a coolant-pump impeller. In this design, the amount of torque transferred to the impeller is controlled based on the quantity of fluid confined within the fluid coupling at any point in time. This quantity can be changed in response to the cooling demand by opening one of two magnetically actuated valves situated in the coolant pump. Opening one valve allows the fluid to move out of the fluid coupling and into a storage chamber; opening the other valve allows the fluid to move back into the fluid coupling. In this approach, the less fluid within the coupling, the less torque is transferred to the impeller, and the less heat is carried away by the coolant.
The inventors herein have observed, however, that the fluid coupling of DE 10 2010 043 264 A1 cannot be drained completely of fluid under normal operating conditions. This is because the design relies on purely rotational forces to move the fluid out from the fluid coupling and into the storage chamber. As a result, the impeller is never completely decoupled from the spinning crankshaft: the pump continues to circulate coolant at a reduced rate even when no coolant flow is desired.
To address this issue and provide still other advantages, the present disclosure provides a coolant pump comprising a drive wheel, a driven wheel, and a coupling-control pump. The driven wheel is connected to a coolant impeller and coupled by a variable degree to the drive wheel, the degree of coupling responsive to an amount of fluid confined between the drive wheel and the driven wheel. The coupling-control pump is configured to change the amount of fluid confined between the drive wheel and the driven wheel based on a variable control signal. This configuration enables the drive wheel of the coolant pump to be completely decoupled from the driven wheel when minimum cooling is desired, for improved fuel economy and emissions-control performance.
The statements above are provided to introduce a selected part of this disclosure in simplified form, not to identify key or essential features. The claimed subject matter, defined by the claims, is limited neither to the content above nor to implementations that address the problems or disadvantages referenced herein.